The present invention relates to an optical element. More particularly, the invention relates to an optical element which electrically functions as a lens using an electro-optic medium.
Technique of optical information processing has been rapidly developed these days, so that it is required to develop an optical element which performs novel functions over the conventional optical elements. For example, an optical element which makes it possible to change the focal distance at a high speed has been required nowadays. For the purpose of achieving such a requirement, there has been developed a variable focal distance lens which is able to change the focal distance thereof by manipulating a mechanical means operationally connected with the lens. However, the conventional variable focal distance lens comprising such a mechanical means for varying the focal distance does not fully satisfy the requirement in the optical information processing field which requires a high speed function of changing the focal distance thereof.
As another means for varying the focal distance of the lens, an electric focal distance varying means is known from the document of Electromagnetic Field Theory Research Group of the Electric Society (EMT-85 No. 16-20, pages 25 to 33). The known electric focal distance varying means comprises a minute refractive index distributed plate type micro lens made from an electro-optic crystal plate in which the refractive index distribution is changed by electo-optic effect of the micro lens so as to vary the focal distance thereof at a high speed.
However, the above mentioned electric focal distance varying means in accordance with the prior art has problems that it is not easy to fabricate the plate type micro lens and that the variable range of the focal distance of the lens is small (about 200 .mu.m).